Simultaneous telegraphy and telephony



(No Model.) 2 Sheets-Sheet 1.

. s. WVHOLMAN.

SIMULTANEOUS TELEGRAPHY AND TELEPHONY. 'No. 510,508;

Patented Dec. 12, 1893.

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WITNESSES.

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UNITED STATES PATENT QFFIGE.

SILAS W". I-IO LMAN, OF BOSTON, MASSACHUSETTS.

SIMULTANEOUS TELEGRAPHY AND TELEPHONY.

' SPECIFICATION forming part of Letters Patent No. 510,508, dated December 12, 1893.

Application filed May 31, 1893.

To 66 whom it may concern:

Be it known that I, SILAS W. HOLMAN, residing at Boston, in the county of Suffolk and State of Massachusetts, have invented certain Improvements in Simultaneous Telegraphy and Telephony, of which the following is a specification.

My invention relates to the simultaneous use of the same wires for both telegraphing and telephoning.

By practicing my invention I may use ordinary telegraph circuits simultaneously and independently as telephone circuits, and this without in any way interfering with the normal action of the telegraph apparatus and without any disturbing noises in the telephone due to the telegraph apparatus.

Heretofore simultaneous telegraphy and telephony have been practiced by introducing'into the telegraph circuit a considerable impedence-or other means of graduating the changes in strength of the telegraph current; the object being to diminish the disturbing noises in the telephone due to the telegraph current. Such devices, in practice, only partially remove this disturbance, and, moreover, do very materially interfere with the proper operation of the telegraph apparatus.

In practicing my invention I do not introduce any impedence into the path of the telegraph current, nor do I in any way graduate or interfere with the normal working of the telegraph current.

Aspecialfeature of my invention is a method of so connecting the telephone apparatus to the telegraph line that the telegraph current shall produce at all times equal potentials atboth tegminals of the telephone, so that two equal and opposite tendencies to disturbance therein shall neutralize each other.

Another special feature used in practicing my invention but not here claimed, as it is described and claimed in another application of even date,- is a double wound electro-magnetic coil, hereinafter more fully described, whose peculiar usefulness arises,in part, from the fact that it offers so great an impedence as to be impermeable to telephone currents tending to pass through the two windings in series and yet oifers no impedence and hence is readily permeable to any kind of currents,

Serial No. 476,091. (No model.)

or to changes in strength of currents, passing through the two windings in multiple, and, in part, from the fact that it acts as an equalizer of two otherwise unequal changes of potential in currents passing through the two windings in multiple. p

In the drawings: Figure 1 is a diagram illustrating the application of my invention to two line wires which are employed separately for the transmission of telegraph signals, and together for the simultaneous transmission of telephone signals. Fig.2 is a dia grammatic view of a convenient form of the double wound electromagnetic coil used in practicing my invention. Fig. 3 is an alternative and somewhat simpler form of Fig. 1 that I find sufficient for use when the telegraph batteries are not excessively strong. Fig. 4: shows two short telegraph lines telephonically connected together in series to form one long telephone circuit, the return being made by one long telegraph line. Fig. 5 shows two shortand independent telephone circuits contrived from successive segments of continuous telegraph lines.

The same letters represent like parts in the same or different figures, numerals being added to the letters to indicate the different parts of the same kind; thus, L represents a linevwire, E an earth, B a battery, K a tele graph key, S a telegraph sounder, X- my newly invented electromagnetic coil, M the core and w the windings of said coil, T a telephone, 19 a telephone terminal and A an artificial line.

The apparatus shown at one end of a diagram is usually the duplicate of apparatus shown at the other end.

' It will be convenient to first describe the double wound electro-magnetic coil used in practicing my invention. Referring to Fig. 2: M is a magnetic core; to is a wire branching at j into two equal wires 10 and 10 one of which wires is wound around the core in one direction (say left-handed), while the other is wound around the core in the opposite direction-(say right-handed). In practice each winding should have a large number of turns so that alone and without the other, it would present a considerable impedence to a vari able current. If itis desired that the ohmic resistance of the coil shall not be large, wire of large sectional area should be used. In practice, also, the core should consist of an annular bundle of soft iron wires to increase the impedence. The peculiar usefulness of this coil arises from the fact that its self induction is so large as to practically prevent the flow of telephone currents through the two windings in series; while the mutual induction of the two windings is such that it practically annuls the effect of the self induction of the single coils when a current flows equally through the two windings in multiple. Thus the coil is impermeable to a telephone current tending to pass over the path to 7 10 and yet is readily permeable to a current, whether constant, intermittent or variable, passing over the wire to and in multiple over the branches w and 10 Moreover, the coil acts as an equalizer of two otherwise unequal changes in potential of currents passing through the two windings in multiple, tending to increase the lesser changes and to decrease the greater, without material loss of energy. Thus, if the changes of potential in branch 20 become greaterthan those in branch 10 the effect of the coil as a whole would be to diminish the greater changes and increase the lesser changes until they become equal. This equalizing effect extends within limits to whatever circuits the windings w and to may be connected. For convenience of construction the windings w and 20 might be parallel wires wound side by side in one direction, but with their opposite terminals connected to 'w, and various other methods of winding will readily suggest themselves to those skilled in the art to which this invention pertains; the desideratum being that two equal currents, whether constant, intermittent or variable, flowing through the two windings in multiple, shall exert equal and opposing magnetizing forces, not onlyon the core as a whole, but upon each portion of the core. In proportion as the above desideratum is attained will the benefits of this feature of my invention be realized.

For convenience in studying the remaining diagrams, I have designated the above described doublc wound electromagnetic coil by the letter X.

Referring now to Fig. 1, L and L are two telegraph lines, the path of the telegraph circuit of L being earth E, battery B, key K, sounder S, coil X, line L, coil X sounder S key Kibattery B and earth E similarly the path of the telegraph circuit of L is B", B K S X L X", S, K B, and E". When the key K is closed, the current from battery B passes equally in multiple circuit through the two windings w and 10 of the coil X (hence without impedence from it), one-half of the current flowing along Land the other half through artificial line A to earth, the artificial line A being approximately equal in resistance, impedence and capacity to the line L. These two branches of the telegraph current simultaneously and equally charge con.-

densers O and (J and, since the whole system is symmetrical, induce through them equal and simultaneous changes of potential at the two terminals 1) and p of the telephone T'. It follows that there will be no disturbing effect in telephone T due to changes in strength of current from battery B. In the same way battery B has no disturbing eifect on telephone T, nor have batteries B and B any disturbing effect on telephone T Experience shows that, on lines of considerable length, the battery at one end has no serious disturbing effect on the telephone at the other end; e. g., batteries B and B have no disturbing effect on telephone T nor have batteries B and B any disturbing effect on telephone T. This I suppose to be due 1n part to the fact that the changes of potential of the end of the line distant from the battery are smaller and much more graduallyattained than are those at the end of the line near the battery; and in part to the equ al1zing effect, as above described, of the windings, e. 9., w and 20 upon the changes of potentials of the portions 0 and O of the circuits with which these windings are connected.

Tracing now the telephone circuit between telephone T and telephone T we find that it starts from terminal 1) of telephone T passes through condenser C, over hue I through condenser C through telephone '1 through condenser C over line L, through condenser C to terminal 19 of telephone T. Telephone currents will not pass through condensers O and O to lines L and L because, in so doing, they would have to pass in series through electro magnetic coils X and X, which we have seen isimpossible. Sim larly, telephone currents on lines L and L w ll not pass through condensers C and C. It 1s true that the artificial lines A and A form ahlgh resistance shunt to telephone T, and slimlarly artificial lines A and A form a high resistance shunt to telephone T but in practice the effect of such loss of telephone energy is small. It is also true that the artificial line A would form a high resistance shunt to the telegraph battery B, and the artificial line A to the battery B which would of course result in a waste of battery current. This waste is, however, avoidable by inserting a condenser in each of the artificial lines, which prevents the passage of the continuous current, but allows that of the wave of current on making or breaking the telegraph circuit by its key. If desired, the loss of telephone energy and of battery current above referred to, may be entirely prevented by omitting the artiticial lines, as shown in Fig. 3. In practice this may be done without introducing any telegraphic disturbance into the telephone, excepting when excessively strong batteries are used to operate the telegraph apparatus. This I suppose to be due to the fact that the first wave of our- IIO rent from battery B e. g., upon closing key K? passes equally in parallel through the two windings of the electromagnetic coil X ,'and, because of the above described equalizing action of the coil, momentarily equally charges condensers O and 0 and consequently the two terminals of telephone T even though the actual flow of current along L is not balanced by a flow along a corresponding artificial line.

Fig. 4 shows two short telegraph lines L and L telephonically connected together 'in series by condenser O to form one lon g telephone circuit, the return being made by the one long telegraph line L". Inasmuch as the undulatory telephone currents will readily pass through condenser O whilethe continuous telegraph currents will not pass through this condenser, it is readily seen that, while keys K and K operate sounders S and S and keys K and K operate sounders S and S and while keys K and K have no effect on sounders S and S as also keys K and K have no efiect on sounders S and S the telephones T and T are in telephonic connection with each other.

Fig. 5 shows two short and independent telephone circuits, one T T and the other T", T, contrived from successive segments of the continuous telegraph lines L and L In order to accomplish this, sounders, wound with a large number of turns of wire such as would naturally be used on telegraph lines of considerable length, are inserted in lines I. and L at S and S Inasmuch as such sounders are opaque to telephonic currents while readily allowing telegraph currents to pass through them, there will be no telephonic communication between telephones T or T on the one hand, and T or T on the other, although telegraph keys K and K will operate sounders S and S and keys K and K will operate sounders S and 8".

In case telephones T and T are separated by considerable lengths of line L and L from any telegraph batteries, they may each be connected to the lines by one pair of condensers as shown. Th us, T connects to line L through condenser C and to L through condenser C as also T connects to L through condenser 0 and to L through condenser 0 the sounderS being between condensers O and C and the sounder S between condensers (J and 0 In case either telephone 'I or T should not be separated by any considerable length of line from a telegraph battery, they should of course be connected to line in the manner described in connection with telephones T and T of Fig. 1.

I claim- 1. In combination with two line wires having telegraph apparatus at each end of each wire and telephone apparatus at each end of the pair of wires; at each end of each l ne wire, a magnetic core, around which the wire from the telegraph apparatus passes by two branches in opposite directions, one of which branches is connected directly to line and also througha condenser to one terminal of the telephone at that end, and the othenof which branches is connected to an artificial line and also through a condenser to the other terminal of said telephone.

2. In combination with two line wires having telegraph apparatus at each end of each wire and telephone apparatus at each end of the pair of wires; at each end of each w1re,a magnetic core, around which the Wire from the telegraph apparatus passes by two branches in opposite directions, one of sald branches being connected directly to line and also through a condenser to one terminal of the telephone at that end, and the other ot said branches being connected through a condenser to the other terminal of said telephone.

3. In a system of simultaneous telegraphy and telephony, a magnetic'core around which the wire from a telegraph apparatus passes by two branches in opposite directions, one of said branches being connected directly to line and also arranged to act inductively upon one terminal of a telephone, and the otherot said branches being connected to an artificial line and also arranged to act inductively upon the other terminal of the same telephone.

4. In a system for simultaneous telegraphy and telephony, a magnetic core around which the wire from a telegraph apparatus passes by two branches in opposite directions, one of which branches is connected directly to line and also to apparatus which acts inductively upon one terminal of a telephone, and

the other of which branches is connected to other apparatus which acts inductively upon the other terminal of the same telephone.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 25th day of May, 1893.

SILAS W. HOLMAN.

Witnesses:

WILLIAM W. J Ac UEs, REUBEN L. ROBERTS. 

